Tech Mysteries: How Did My Hard Drive Shrink?

You buy a new 2 TB external hard drive at the store, plug it into your computer and notice that the hard drive properties list the size not as 2 TB but as something a bit less — 1.9 TB. There are two reasons that this can happen: pre-installed software and marketing.

Some hard drives today, particularly external drives marketed as backup devices, ship pre-loaded with special software ostensibly designed to make backing up your computer easier. Depending on your practice and your level of technological sophistication, this may be a boon — no need to mess around with complicated third party software to make sure your data is properly backing up.

If you already have backup software, or if you plan to use the drive for something other than backup, the pre-installed software is simply wasted space. You can reclaim that space by reformatting the drive and starting fresh.

What about marketing? Historically, computers count storage using base 2 rather than base 10: That means a kilobyte is 1,024 bytes rather than 1,000, a megabyte is 1,024 kilobytes, and so forth. Hard drive manufacturers, on the other hand, have long used base 10 to market the capacity of their devices. So the 2 TB drive you buy off the shelf actually has a capacity of 2,000 gigabytes rather than the 2,048 your computer expects.

There’s good news for Mac users: Apple started using base 10 to measure storage as of OS 10.6, so what you see on the box is what you’ll get on your device (pre-installed software aside).

Have a tech mystery you’d like explained? Use the contact form to share it with us and the answer may be featured in a future blog post.


A version of this article originally appeared in YourABA, a free monthly eNewsletter for ABA members.

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